Client Background#
The customer is a large manufacturer of mining equipment. Its gearboxes run under continuous heavy-duty service, and the unit covered by this project operated at a noise level of 92 dB. Noise at that level affected the working environment around the machine and shortened the service life of the gear components inside the box. In a gearbox of this class the gear pair is the main source of excitation, so the improvement work started from the tooth geometry and the manufacturing process rather than from the housing.
Requirement & Challenge#
- Reduce the operating noise of the gearbox
- The original gear set was produced by gear hobbing only, so tooth accuracy was low, at GB grade 8
- The tooth profile carried no modification, and the meshing impact at each engagement was significant
- Tooth surface roughness was coarse, at Ra ≥ 3.2 μm
- Extend gear service life and lengthen the maintenance interval, which stood at 3 months
Solution & Process#
- Gear parameter redesign - Gear parameters were redesigned so that the contact ratio was optimised and the variation of mesh stiffness reduced. A higher contact ratio shares the load between more tooth pairs at any single moment, which lowers the dynamic load carried by each flank.
- K-type profile modification - A K-type modification of 0.02~0.04 mm was applied to the tooth profile. The modification compensates for tooth deflection under load and softens the transfer of load from one pair of teeth to the next, so the meshing impact is no longer a sudden step.
- Upgrade from hobbing to grinding - The manufacturing route was changed from gear hobbing to gear grinding, raising tooth accuracy to DIN 5 grade. Grinding after heat treatment removes the distortion left behind by hobbing and hardens the flank in a controlled geometry.
- Tooth surface finish - Grinding also brought the tooth surface to Ra ≤ 0.4 μm, cutting friction and the noise excitation that follows from a rough flank.
Result & Feedback#
- Operating noise came down from 92 dB to 78 dB, a reduction of 14 dB
- Gear life was extended by 40%
- The maintenance interval moved from 3 months to 12 months
